import java.util.Scanner;

public class c2 {
    //定义三个有参数无返回值方法，分别实现计算三角形、正方形、长方形的面积。
    public static void main(String[] args) {
        chanfgangxing(6,9);
    }
    public static void chanfgangxing(double a,double b) {
        Scanner scanner = new Scanner(System.in);
        double S = a * b;
        System.out.println(S);
    }
    public static void zhengfangxing(double h) {
        Scanner scanner = new Scanner(System.in);
         double S = h * h;
        System.out.println(S);

    }
    public static void sanjiapxing(double a,double h) {
        Scanner scanner = new Scanner(System.in);
        double S = 1 / 2 * a * h;
        System.out.println(S);
    }
}
